BIOL1421: Chapter 19 (The Cardiovascular System; The Heart)

HEART OVERVIEW / HEART CHAMBERS
-heart is divided into four chambers (right side and left side, atrium is top and ventricle is bottom)
-tricuspid valve and bicuspid valve
-left side has clean oxygenated blood, right side has dirty deoxygenated blood

-left artery (aorta) takes oxygenated blood from ventricle (blood originating from lungs) → tissues throughout body, blood is red
- right artery takes deoxygenated blood from ventricle → lungs, blood is dark (gives it CO2 and oxygen)
(through pulmonary trunk)

-blood → heart : carried by veins, brings blood back to atrium

1.) right atrium receives deoxygenated blood → right ventricle
2.) right ventricle → lungs
3.) left atrium receives oxygenated blood → left ventricle
4.) left ventricle → gives oxygenated blood throughout entire body

LOCATION OF HEART
-heart is located between lungs and superior to diaphragm
(sits between the 2nd -and 5th rib)
-heart is also located between sternum and the thoracic vertebrae
-inside the thoracic cavity/cage

HEART WALL
-three layers of heart: (most superficial) epicardium, myocardium, endocardium (deepest)
-myocardium (thickest layer, muscle tissue; causes continuous contractions)
(left side myocardium is thicker than right side, to pump blood to different regions of the body)
-entire sac: pericardium (inner layer: visceral pericardium, outer layer: parietal pericardium)

CARDIAC MUSCLE TISSUE
-cardiac muscle fibers are short, branched, striated, and contain uni-nuclear cells
-intercalated discs connects action potentials and produces contractions

HEART VALVE ANATOMY
1.) bicuspid/mitral valve (between left atrium and left ventricle)
2.) tricuspid valve (between right atrium and right ventricle)
3.) aorta valve: beginning of artery (left side)
4.) pulmonary valve: beginning of pulmonary trunk (right side)
-2 semilunar valves: takes blood from arteries (prevent backflow of blood)
-no valve in veins

HEART INTERNAL ANATOMY
-interventricular septum: muscle separating the right and left ventricles
-papillary muscles: muscles at base of ventricles, attached to chordae tendinae
(chordae tendinae position changes during contraction/relaxation)
-conus arteriosus: beginning of pulmonary trunk
-moderator band: located around right side of ventricle

BLOOD FLOW THROUGH THE HEART (atrium → ventricle)
-2 av valves (bicuspid and tricuspid valve)
-when two ventricles contract → semilunar valve, right part puminary valve

BLOOD FLOW OUT OF HEART
(right side) blood enters → pulmonary trunk (through pulmonary arteries) → lungs
(left side) blood enters → aortic arch (through aortic arteries) → body tissues

BLOOD FLOW INTO HEART
(left right) aorta artery gives oxygen to entire body
(good blood given to heart through superior vena cava)

CONDUCTION SYSTEM (starts from nodes)
-regulates constant pumping of the heart
(regulates electrical impulses that make the heart beat)
-impulse begins in sinoatrial node (SA node) → atrioventricular node (AV node) → bundle of His → branches to other parts of the ventricle → Purkinje fibers → contraction is produced, heart ejects blood

-muscle cells control contractions

ELECTROCARDIOGRAM
P (represents activity of atrium)
QRS (represents activity of ventricle)

CARDIAC CYCLE
systole: when both ventricles contract
diastole: when both ventricles relax/expand
(diastole longer than systole)

ggggg

ggggg

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CIRCULATION PATHWAY
artery (red, takes blood away from heart); vein (blue, takes blood towards heart)
1.) deoxygenated blood in right atrium
2.) (triscuspid valve) → right ventricle
3.) (pulmonary valve) → pulmonary trunk and arteries

4.) in pulmonary capillaries, blood gains O₂ and loses CO₂

5.)

INTRODUCTION OF THE HEART
The heart is a double pump
1.) left side pumps oxygenated blood → entire body, through blood vessels
2.) right side pumps deoxygenated blood → lungs, to pick up oxygen and unload carbon dioxide

LOCATION OF HEART
-located in mediastinum of thoracic cavity
(anatomical region between lungs, extending from sternum, to the vertebral column)
-sternum (anterior) and vertebrae (posterior)
-situated obliquely, between the lungs
(apex, pointed end that is directed inferiorly to the left; base positioned superiorly to the right)

-pleura: holds the lungs
-superior vena cava: receives deoxygenated blood (from neck)
-inferior vena cava: receives deoxygenated blood (other parts of body)
(veins that bring deoxygenated blood back to heart)

MEMBRANE LAYERS OF THE HEART
Pericardium is the protective membrane structure (sac) that surrounds the heart.
The two primary components of the pericardium include:
1.) fibrous pericardium - outer layer of membrane; tough, dense irregular connective tissue (prevents overstretching and anchors heart in mediastinum)

2.) serous pericardium - inner layer of membrane; delicate double layer serous membranes filled w/ serous fluid in pericardial cavity between membrane layers
The double layer serous membrane includes:
-parietal layer, outer serous layer that is fused to fibrous pericardium
-visceral layer (epicardium), inner serous layer that attached to heart muscle tissue
-pericardial fluid, thin slipper lubricating serous fluid

LAYERS OF HEART WALL
The three layers of the heart wall includes:
1.) epicardium (visceral serous layer) - superficial visceral layer of the pericardium; contains blood and lymphatic vessels that supply the heart muscle

2.) myocardium - middle cardiac muscle tissue layer; has involuntary cardiac muscle fibers organized in bundles that swirl diagonally around the heart

3.) endocardium - endothelium layer overlying connective tissue; lines heart chambers and heart valves; continuous with endothelia lining blood vessels

aorta (brings blood away from left)
pulmonary trunk (brings blood away from right atrium)

HEART CHAMBERS
The four heart chambers include:
1-2.) Two atria (receiver) - upper chambers receive blood from veins; has pouchlike auricles on anterior surface that increases blood volume capacity

3-4.) Two ventricles (pumper) - lower chambers pump blood into arteries

The heart chambers are surrounded by sulci, which are surface grooves that contain the blood vessels and fat.
-eg. coronary sulcus, anterior interventricular sulcus, posterior interventricular sulcus

-brachiocephalic trunk - gives oxygenated blood to head and neck
-(right and left) carotid artery - gives oxygenated blood to left and right side head and neck
-subclavian artery -

-superior vena cava - receives deoxygenated blood from head and neck → right atrium
-inferior vena cava - receives deoxygenated blood from rest of body → right atrium

“pulmonary”: relating to lungs

three parts of aorta
-ascending aorta brings oxygenated blood to heart muscles
-arch of aorta brings oxygenated blood to head neck shoulders (left common carotid artery, left subclavian artery, brachiocephalic trunk)
-descending aorta

aorta has two other branches (coronary, brings deoxygenated blood back to heart muscle)

(1) RIGHT ATRIUM
The right atrium receives blood from superior vena cava, inferior vena cava, and coronary sinus (from the heart itself)
-separated internally from left atrium by interatrial septum (contains fossa ovalis, fetal foramen ovale which is open as child and closes as adult)
-has smooth posterior wall, but pectinate muscle ridges anteriorly extending into auricle
-blood passes through triscuspid valve (right atrioventricular valve) → right ventricle

(2) RIGHT VENTRICLE
The right ventricle receives blood from right atrium.
-separated internally from left ventricle by interventricular septum
-interior of chambers has ridges, raised bundles of cardiac muscle called trabeculae carneae
-cusps of tricuspid valve connected to
1.) chordae tendinae: tendon-like cords
2.) papillary muscles: cone-shaped trabecular carneae
-pumps blood (through pulmonary valve or semilunar valve) → pulmonary trunk that carries blood to the lungs

(3) LEFT ATRIUM
The left atrium receives oxygenated blood from four pulmonary veins
-located on the other side of interatrial septum and arrangement of pectinate muscles
-blood passes through bicuspid/mitral valve (left atrioventricular valve) → left ventricle

(4) LEFT VENTRICLE
The left ventricle receives blood from left atrium.
-located on other side of interventricular septum and same arrangement of chardae tendineae and papillary muscle for bicuspid valve cusps
-pumps blood through aortic valve (semi lunar valve) → ascending aorta carries blood → heart wall and rest of body

-ligamentum arteriosum connects aorta to pulmonary trunk; a remnant of fetal blood vessel (ductus arteriosus) that shunted blood from the pulmonary trunk → aorta, bypassing nonfunctioning fetal lungs

MYOCARDIAL THICKNESS AND FUNCTION
-thickness varies among chambers related to their function
-atrial walls thinner than ventricular walls, delivering blood → ventricles, with gravity assist
-left ventricle wall thicker than right ventricle wall
(left ventricle pumping blood great distances → all parts of body in systemic circulation VS right ventricle only pumping blood to lungs short distance through pulmonary circulation)

HEART VALVES
Heart valves open and close, in response to pressure differences across valves, created when chamber of heart contracts or relaxes.
-blood flows from areas of high pressure → low pressure
-contraction of chamber increases pressures

Heart valves ensure one-way flow of blood and contains two types of valves (four total).
1.) atrioventricular valves - between atrium and ventricle
-eg. tricuspid valve and biscuspid valve
2.) semi-lunar valves - between ventricle and artery
-eg. pulmonary valve and aortic valve

ATRIOVENTRICULAR VALVES
The atrioventricular valves are the tricuspid valve (right) and biscuspid valve (left).

When opened, rounded ends of cusps project into ventricle chamber.
-papillary muscles in ventricle are relaxed and chordae tendineae are slack
-blood moves through from higher pressure in atria

When closed, ventricle contracts.
-pressure of blood in chamber drives cusps upwards, until edges meet and close valve
-contraction of papillary muscles tightens the chordae tendineae, preventing valve cusps from pushing up into atria chamber and backflow of blood

SEMILUNAR VALVES
The semi-lunar valves are the pulmonary valves (right) and aortic valves (left).
-contains three moon-shaped cusps prevent backflow

Opened when pressure in ventricles exceeds pressure in arteries, as ventricles contract

Closed when ventricle relaxes and back-flowing blood fills the valve cusps
-blood in cusp causes semilunar valves to contact each other tightly and close the opening
-prevents backflow of blood from arteries
-no similar valve between veins and atria - atrial contraction compresses those openings (blood doesn’t flow from atria → veins)

ARTERIES AND VEINS
-pulmonary artery carries blood away from the heart; blue in color because it carries blood that low in oxygen
-pulmonary vein brings blood to the heart; red in color because it transports oxygen-rich blood from the lungs

CIRCULATIONS
-flow of blood with each heart beat
-two separated closed circuits (so oxygen-rich and oxygen-poor blood do not mix)
-two circuits in series, (so output of one becomes the input of other)
1.) pulmonary circulation - blood circulation involved with lungs
2.) systemic circulation - oxygenated blood circulation involved with cells throughout the body

3.) coronary circulation - oxygenated/deoxygenated blood circulation involved moving back into heart muscles

PULMONARY CIRCULATION
-right side of heart is pump
-circulation of oxygen-poor blood through the lungs (unloads CO2 and picks up O2 through gas exchange)
-right ventricle ejects blood → pulmonary trunk → pulmonary arteries and capillaries
-pulmonary veins carry blood back to → left atrium

SYSTEM CIRCULATION
-left side of heart is pump
-circulation of oxygen-rich blood through the body (delivers O2 to all body cells, except for air sacs in lung, and picks up CO2)
-left ventricle ejects blood → aorta (through systemic arteries) and capillaries
-systemic veins carry blood back → right atrium

CORONARY CIRCULATION
The right and left coronary arteries branch from ascending aorta to supply oxygen-rich blood to myocardium oh heart
-branches extend in sulci, to both atria/ventricle chambers, right/left, and anterior/posterior
-anastomoses are connections that form where two or more arteries supply the same body region to provide alternate routes in case of obstruction

Coronary capillaries exchange gases and nutrients/wastes.

Coronary veins collect oxygen-poor blood → coronary sinus (on posterior of heart) → emptying into right atrium

-right coronary artery → marginal artery branch
-left coronary artery → circumflex artery → (1) posterior interventricular branch or (2) anterior interventricular branch

CARDIAC MUSCLE TISSUE
Cardiac muscle fibers are connect end-to-end via intercalated discs
-in between, there are desmosomes that provide strength
-in between, there are gap junctions that allow muscle action potentials to conduct from one muscle fiber to its “neighbor”

1.) autorhythmic fibers - form the cardiac conduction system; spontaneously depolarize and generate action potentials
2.) contractile fibers - produce powerful contractions that proper blood

CARDIAC CONDUCTION SYSTEM
Sinoatrial (SA) node pacemaker sets the rhythm of electrical excitation
Conduction system provides path for each cycle of cardiac excitation

The blood path through the heart:
SA node → AV node → AV bundle → bundle branches → Purkinje fibers

CONTRACTION OF CONTRACTILE FIBERS
The mechanism of cardiac contraction similar to skeletal muscle.
The phases of the action potential includes:
1.) depolarization - Na+ channels open and ions inflow
2.) plateau - Ca2+ channels open, inflow triggers contraction
3.) repolarization (when muscles relax) - K+ channels open and ions outflow

-electrical activity

ELECTROCARDIOGRAM (ECG OR EKG)
-recording of the electrical charges that accompany each heartbeat
Normal ECG has three waves that include:
1.) P wave - atrial depolarization
2.) QRS complex - ventricular depolarization
3.T wave - ventricular repolarization

CORRELATION OF ECG WAVES WITH HEART ACTIVITY
diastole - atrial and ventricular relaxation
systole - atrial and ventricular contraction

Sequence of systole and diastole includes:
1.) depolarization of atrial (P wave)
2.) atrial systole occurs
3.) ventricular depolarization (QRS complex)
-also masks atrial repolarization occurring at same time
4.) ventricular systole begins; atrial diastole begins
5.) ventricular diastole occurs

CARDIAC CYCLE
All events associated with single heartbeat
-two atria contract (systole) and relax (diastole)
-two ventricles contract (systole) and relax (diastole)

Heart sounds are caused by blood turbulence due to closing of valves
-lubb sound (S1): closure of both AV valves, as ventricles contract (ventricle systole); ventricles contract to give blood to arteries
-dupp sound (S2): close of both SL valves, as ventricles relax (ventricular diastole); ventricles relax so blood can flow into ventricle

PRESSURE AND VOLUME CHANGES DURING CARDIAC CYCLE (ATRIAL SYSTOLE)
Two atria contract (systole) and ventricles are relaxed (diastole)
-stimulated by action potential from SA node, marked by P wave of ECG
-exert pressure on blood in chamber, forcing blood (through open AV valves) → ventricles

SL valve still closed, ventricles fill
End of atrial systole is also end of ventricular diastole - volume of blood called end-diastolic volume (EDV)
-maximum amount of blood that ventricles can receive from atrium

SA node (represented by P wave)→ AV node → AV bundles (bundle of His) → bundle branches → Purkinje fibers (related to AV valve)
(produces fast action potential)

Two ventricles contract (systole) and atria relax (diastole)
-stimulated by action potential from Purkinke fibers, marked by QRS complex of ECG
-exert pressure on

Volume of blood remaining in ventricles is end-systolic volume (ESV)


During contraction (systole), SL valve close and AV valve open to receive blood (causing ventricle to expand)
-eventually AV valve close and SL valve opens to pump blood out

CARDIAC OUTPUT
Cardiac output is the volume of blood ejected each minute from left ventricle → aorta OR right ventricle → pulmonary trunk

Cardiac output (CO) = stroke volume (SV) x heart rate (HR)
-SV is the volume of blood ejected by the ventricle during each contraction (or beat)
-HR is the number of heartbeats per minute

Entire blood volume flows through pulmonary and systemic circulation each minute
CO changes to meet needs, changing with exercise and anything that modifies SV or HR

BLOOD PRESSURE MEASURING
systolic pressure: maximum blood pressure during contraction of ventricles
diastolic pressure: mininum pressure recorded just prior to next contraction

REGULATION OF STROKE VOLUME (SV)
The three factors that regulate and ensure equal volumes of blood being pumped from right and left ventricles
1.) preload - stretch on the heart before it contracts
2.) contractility -forcefulness of contraction influenced by ANS, hormones, Ca2+ concentration
(when preload and contractility increase, stroke volume increase)
3.) afterload - pressure that must be exceeded before the SL valves open and ventricular ejection begins
(when afterload increases, stroke volume decrease)

REGULATION OF HEART RATE (HR)
The cardiovascular center in medulla oblongata is origin of nervous system regulation of HR.
-receives input from proprioceptors, chemoreceptors, and baroreceptors
-also input from limbic system and cerebral cortex
-autonomic regulation

Chemical regulation of HR
-hormones (like epinephrine and norepinephrine) from adrenal gland, thyroid hormones
-cations (ionic imbalances of Na+, K+, and Ca2+)

Other factors
-age, gender, physical fitness, and body temperature

AUTONOMIC REGULATION OF HEART RATE
Sympathetic
-cardiac accelerator neurons arising from the cardiovascular center enervate SA node, AV node, and most of myocardium
-release norepinephrine
-increase heart rate and force of contraction

Parasympathetic
-neurons arising from the cardiovascular center reach heart (through vagus nerve) → SA node → AV node → atrial myocardium
-release acetylcholine
-